Apparatus for preparing a biaxially oriented thermoplastic article

ABSTRACT

Apparatus for preparing a biaxially oriented thermoplastic article, particularly a bottle useful in bottling liquids under pressure such as carbonated beverages. The apparatus is comprised of a sliding mold, an annular extrusion orifice located within the mold cavity, means for extruding a hollow slug through the extrusion orifice, means in the mold to accept the extruded slug, means for sliding the mold from a first location to a second location relative to the extrusion orifice while the slug is continuously extruded to draw the extruded slug into the interior of the mold forming a hollow shell out of the extrudate, and means to introduce a fluid into the interior of the hollow shell while the slug is being extruded to expand the hollow shell against the interior of the mold.

I United States Patent 11 1 1111 3,778,214

Wyeth et al. Dec. 11, 1973 APPARATUS FOR PREPARING A 3,160,130 12/1964Pesak 425/387 x BIAXIALLY ORIENTED THERMOPLASTIC e a yma e ARTICLE3,337,910 8/1967 West 425/387 X [75] Inventors: Nathaniel Convers Wyeth,3,349,155 10/1967 Valyi .1 425/468 X Mendenhall Ronald Newman Weber XRoseveare, Lynchburg, Va. Primar Examiner-J. S encer Overholser [73]Asslgnee: du P0nt.de.Nemours and Assistafzt Examiner-MiEhael 0. SuttonCompany wllmmgton Attorney-Louis Del Vecchio [22] Filed: June 14, 197221 Appl. No.: 262,593 [571 ABSTRACT Related U S Application DataApparatus for preparing a biaxial'ly oriented thermoplastic article,particularly a bottie useful in bottling [60] 22 22 E1 9 liquids underpressure such as carbonated beverages. 2 5; gg g sg i The apparatus iscomprised of a sliding mold, an annua one lar extrusion orifice locatedwithin the mold cavity, [52] U 8 Cl 425/326 425/387 425/DIG 206 meansfor extruding a hollow slug through the extru- [51] hit Cl 1' B29d2.3/03 siOn orifice, means in the mold to accept the extruded [58]Fie'ld 387 249 slug, means for sliding the mold from a first location ito a second location relative to the extrusion orifice while the slug iscontinuously extruded to draw the extruded slug into the interior of themold forming a hol- [56] References Clted low shell out of theextrudate, and means to introduce UNITED STATES PATENTS a fluid into theinterior of the hollow shell while the 3,288,898 11/1966 West 425/326Xlug is being extruded to expand the hollow hell 217061308 4/1955 againstthe interior of the mold. 2,810,934 l0/l957 3,002,225 10/1961 Goller425/387 X 31 Claims, 13 Drawing Figures l\ I Y m )1 PATENIED BEE I 1 W5SHEETIUFG F IG-l- PATENIED 3.778214 SHEET 2 BF 6 T0 SOURCE OFPRESSURIZED 2 53 F I G- 2 FLUID [*START CONTRO l EXH.

MOVE M0 D SERVO AMPLIFIER ND SERVO 40 APPARATUS FOR PREPARING ABIAXIALLY ORIENTED THERMOPLASTIC ARTICLE CROSS REFERENCE TO RELATED CASEThis application is a division of U. S. Pat. application Ser. No.93,571, filed Nov. 30, 1970, now U.S. Pat. No. 3,733,309 which is inturn a continuation-in-part of U. S. Pat. application Ser. No. 885,853,filed Dec. 17, 1969, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to an apparatus forpreparing molecularly oriented thermoplastic articles and particularlybottles useful in containing liquids under pressure such as sodas, beerand aerosols.

In preparing the thermoplastic articles, it is desirable to minimize theamount of thermoplastic polymer used to make the article while stillmaintaining properties in the article sufficient to render the articleuseful for its intended purposes. For example, in a bottle for use incontaining liquids under pressure, it is desirable to make the shell asthin as practical while still retaining sufficient strength in the shellto contain the liquid and the internal pressure.

One way of improving the physical strength properties of acrystallizable thermoplastic is to molecularly orient the thermoplasticpolymer thereby permitting the use of reduced amounts of polymer for theequivalent strength properties otherwise exhibited by a relativelyincreased amount of unoriented polymer. Orientation can be accomplishedby stretching the polymer at the orientation temperature of the polymer,i.e., below its crystalline melting point. While stretching isaccomplished rather easily on a flat sheet, it is difficult toaccomplish on a shaped article such as a bottle; and it is particularlydifficult to biaxially orient such an article.

There is a need, therefore, for a practical and efficient apparatus forproducing a biaxially oriented, shaped, thermoplastic article havingimproved strength properties.

SUMMARY OF THE INVENTION Accordingly, the present invention provides anapparatus for producing a hollow, biaxially oriented, thermoplasticarticle having improved strength properties.

The apparatus of this invention consists essentially of:

a. a slidable mold having a cavity shaped to reproduce a desirablearticle,

b. an annular extrusion orifice located within the mold cavity,

0. means for extruding a hollow thermoplastic slug through the annularextrusion orifice into the mold,

d. means in the mold to accept and hold the extrudate at one end of themold cavity,

e. means for sliding the mold from a first location to a second locationrelative to the extrusion orifice while the thermoplastic slug iscontinuously extruded and drawn into the interior of the mold forming ahollow shell out of the extrudate,

1. means for introducing a fluid against the interior of the hollowshell, while the slug is simultaneously being extruded and drawn, toexpand the hollow shell of extrudate against the interior of the mold,and, if needed as when using an open-ended slug,

g. means for urging the trailing edges of the slug radially inwardtoward the center of the article forming an integral closure.

DESCRIPTION OF THE DRAWINGS:

FIG. 1 is a perspective view of the apparatus of this invention,including means for actuating moving parts of the apparatus.

FIG. 2 is a schematic diagram of the principal parts of the apparatus ofFIG. 1 showing hydraulic, fluidic and electrical circuits for actuatingand controlling the apparatus.

FIG. 3 is a fragmentary cross-sectional view of the apparatus of thisinvention positioned during the initial stage of forming a hollowarticle and specifically showing an annular bead being formed.

FIG. 4 is a fragmentary cross-sectional view of the apparatus of thisinvention positioned during the intermediate stage of forming a hollowarticle and specifically showing the crucial step of combined nonmoltenextrusion and expansion by use of internal fluid forces.

FIG. 5 is a fragmentary cross-sectional view of the apparatus of thisinvention positioned after the hollow article has been completelyformed.

FIG. 6 is an enlarged fragmentary cross-sectional view of a portion ofthe positioned apparatus shown in FIG. 5 showing in greater detail theregion around the annular extrusion orifice near the completion of thecombined extrusion and expansion operation.

FIG. 7 is an enlarged fragmentary cross-sectional view similar to thatof FIG. 6 but showing the region around the annular extrusion orificeupon the completion of the hollow article formation.

FIGS. 8 and 9 are fragmentary crosssectional views of the apparatus ofthe invention adapted to handle polymers with poor conformability to themold.

FIG. 10 is a bottle formed in the apparatus of FIG. 9.

FIG. 11 is a fragmentary cross-sectional view of an alternate embodimentincorporating a sliding center rod with the center rod in its fullyextended position.

FIG. 12 is a fragmentary cross-sectional view of the alternateembodiment shown in FIG. 11 with the center rod at an intermediate stageof withdrawal corresponding relatively to the intermediate position ofthe sliding mold.

FIG. 13 is a fragmentary cross-sectional view of the alternateembodiment shown in FIG. 11 with the center rod completely withdrawncorresponding relatively to the final position of the sliding mold.

DETAILS OF THE INVENTION The apparatus of this invention. useful inpreparing thermoplastic articles will be described in detail with theaid of the drawings. Referring to FIGS. 3 to 5, a hollow, cylindricallyshaped, thermoplastic polymeric slug 1 described below is first placedin an extrusion chamber 2 formed by the bore of an extrusion barrel 3and the outside cylindrical surface of a center supporting rod 4. A moldcavity 5 of mold 6 has an internal configuration such as the shape ofthe article desired and is positioned in a first location surroundingthe extrusion barrel 3 as is particularly shown in FIGS. 1 and 3. Themold cavity 5 illustrated in FIG. 3 is one for use in fabricating anarrow neck bottle such as can be employed in bottling carbonatedbeverages.

The extrusion barrel 3 is in axial alignment with a mandrel 7 having auniform outside diameter that is substantially the same as the insidediameter of the neck of the bottle being fabricated. A fluid passage 8is contained within the mandrel 7 having fluid exit ports 9 and 10 atthe end of the mandrel 7 that is in closest proximity to the extrusionbarrel 3. Situated between the end of the barrel 3 and the end of themandrel 7 is an annular extrusion orifice 11. This office canconveniently be formed by rounded end 12 of the extrusion barrel 3 andannular flared piece 13 which is attached to the body of the mandrel 7.

The annular extrusion orifice 11, shown in detail in FIGS. 6 and 7, isdefined by the confronting end portions of the extrusion barrel 3 andthe mandrel 7. In cross-sectional profile, wherein the cross section istaken coplanar with the central axis of extrusion, as shown in FIGS. 6and 7, both members are machined with a curving shape to provide asmooth transition from the annular extrusion chamber 2 outwardly and toprovide a boundary for the annular extrusion orifice 1 1 such that theorifice is always convergent in its crosssectional area. The orificebecomes progressively smaller in the direction of flow out to the outerboundary of its extrusion annulus which is proximate to the periphery ofthe mandrel 7 from which the polymer emerges from the annular extrusionorifice 11 to enter the cavity 5 of the mold 6. Since the orifice isconvergent in the direction of extrusion, it follows that thecross-sectional area of the orifice taken perpendicular to the directionof extrusion can either be the same or decrease in the direction ofextrusion.

Referring to FIG. 6, the dimension of the orifice 11 measured axially isshown as T. In this figure, as in FIG. 7, the size of this dimension isenlarged for descriptive reasons. In an actual apparatus, the dimensionT can range from about 0.01 to 0.075 inch depending on thecharacteristics of the polymer being formed and on the degree oforientation to be imparted. The orifice serves as the locus for highrate work input to the polymer that raises the temperature of thepolymer to the orientation temperature range of the polymer, insuringgood orientation characteristics. In general, thedegree of orientationof the extrudate increases as the ratio increases between the averagediameter of the extrudate as it emerges from orifice 11 and the averagediameter of the slug.

The annular extrusion orifice 11 is area-convergent, as shown, in orderto insure stable flow and a finite pressure drop between chamber 2 andthe outer part of the orifice 11 during extrusion and especially at thetime closing of the end of the bottle article is initiated; statedsomewhat differently, a high pressure in the chamber 2 at the instantthat the rod 4 is withdrawn, assures that polymer will flow inwardlyfrom the chamber 2 (with the continued urging of the ram effecting aclosure.

The mold cavity 5 has an annular groove 14 within its contour that isinitially located adjacent to the discharge side of the annularextrusion'orifice 11. The mold 6 with its mold cavity 5 can also bemoved from the first location shown in FIG. 3 to a second location shownin FIG. 5.

Referring to FIGS. 1 and 2, the means for moving the various parts ofthe apparatus generally comprise hydraulic cylinders or hydraulic-motorswhich are situated on a frame 25. The extrusion barrel 3 is flangemounted on a shelf 26 and is concentrically aligned with the hollowextrusion ram 15 which operates through an opening, not shown, in theshelf 26. Beneath the shelf 26 the ram 15 is aligned with and joined tothe hollow tubular piston rod 28 of a nondifferential, or doubleextended type, hydraulic motor 29 which is secured to the frame 25.Inside the bore of the extrusion ram 15 is the center supporting rod 4which extends from the top of the extrusion barrel 3 entirely throughthe extrusion ram 15 and the tubular piston rod 28. Beneath the lowerend of the piston rod 28 the center supporting rod 4 is joined to thepiston rod of another hydraulic motor 30 which is likewise secured tothe frame 25. 1

At the upper end of the frame 25 is a dovetail slide 31 arranged to bemoved parallel to the axis of the barrel 3 by means of a hydraulic motor32 the body of which is secured to the shelf 26. Joined to the slide 31is beam 33 which supports the mandrel 7 in axial alignment and spacedrelationship with the extrusion barrel 3. Extending outward from theframe 25 is a fixed bifurcated stripping fork 34, the tines of whichstraddle the mandrel 7 directly beneath the beam 33. The mandrel 7 canbe raised vertically by means of the motor 32 to effect the stripping ofa formed container, not shown, from the mandrel. Additionally, thisaction exposes the extrusion chamber 2 in the barrel 3 to permit theinsertion of a new slug of plastic.

Surrounding both the mandrel 7 and the extrusion barrel 3 is a piecedmold 6 having apertures in its upper and lower extremities axiallyaligned with and slidable on both of these members. Mold 6 is movablevertically by use of hydraulic motor 35 the body of which is secured tothe shelf 26. In FIGS. 1 and 2, the mold 6 is shown in its lowermostlocation, positioned for the initiation of a cycle. The mold 6 comprisestwo generally symmetrical halves with a planar parting face. The halvesare hinged as shown in FIG. 1 but could be mounted on slides or links topermit the opening and closing on the extrusion barrel 3 and the mandrel7. It should be understood that a movable clamping means, not shown,must be provided to secure the halves of the mold to each other toresist internal pressures of considerable magnitude. Such clamping meansare well known in the art and generally comprise latches, pneumatic orhydraulic motors, screw clamps or the like. It will be understood thatthe mold walls may be made porous.

The mold parts may require heat or refrigeration depending on thematerial of the slug and may be provided with individual jackets orpassages, not shown, for electrical or fluid heating or cooling. Theextrusion barrel 3 may also require heat or refrigeration and jacket 36is shown surrounding the part of the extrusion barrel that is accessiblebeneath the mold 6. If desired, the mandrel 7 can be equipped similarly.

Referring to FIG. 2, the hydraulic motors are controlled sequentially bymeans of several solenoid operated valves and an electrical controlcircuit. A gear pump 38 supplies fluid under pressure from a sump 39 toa plurality of conduits 40. The principal hydraulic motor is motor 29which drives the ram 15 at a velocity determined by the profile of thecam 23. Cam 23 is carried on arm 27 by the rod 28 and is used toposition a potentiometer 51 to produce a position-indicative outputvoltage. This output voltage is fed to servo control 44 which, in turn,controls the operation of the valve 43 by varying the rate of flow offluid to the motor 29 via valve 41 in proportion to the output voltage,the

voltage and the fluid flow being higher when the high part 23b of thecam 23 is reached. The valve 41 is a self-centering four-way solenoidvalve having ports which are blocked as shown whenthe solenoids are notenergized. When the solenoid 42a is energized, the valve 41 swingsclockwise admitting fluid to port 29a of motor 29 .while simultaneouslyopening port 29b to exhaust, thus permitting fluid in the upper part ofmotor 29 to return to the sump 39 via a conduit, not shown. Theadmission of fluid to port 29a causes the ram 28 to be driven upward.When the opposite solenoid 42b is energized, the valve 41 will movecounter clockwise and drive the ram 28 down again.

The arm 27 on piston rod 28 also drives the movable part of apotentiometer 24 which produces and output voltage proportional to theposition of the rod 28 and ram 15 and varies in magnitude. This varyingsignal is used for controlling several events to be described. Thesystem is activated by means of a power control circuit 45 whichsupplies electrical energy from source 46 directly to solenoid 42a onvalve 41 and simultaneously to voltage comparison circuit 47 which alsoreceives the input voltage from the potentiometer 24. The circuit 47 isadapted to produce three different outputs sequentially depending on themagnitude of the voltage output of the potentiometer 24 which depends onthe position of the rod 28 of the motor 29. Thus, as the rod and rammove, the following events occur in sequence:

1. The mold 6 is set in motion upward at a constant velocity by means ofmotor 35 via valve 49 which is actuated by solenoid 50a.

2. A short time later, pressurized fluid is admitted via solenoid valve52 and needle valve 53 to mandrel 7, passage 8 and ports 9 and at acontrolled rate of flow.

3. Near the end of the stroke of the ram 15, the mold stops at the endof the stroke of cylinder 35 and the center supporting rod is thentriggered into action by a signal from circuit 47 to solenoid 54a. Thiscauses valve 55 to admit pressurized fluid to the upper port 30a ofmotor 30 thus causing the center supporting rod 4 to be pulled downward.It should be understood that the stroke of the motor 30 is very short,such as 0.1 to 0.2 inch. Thus, this motor and the rod 4 quickly bottomin the downward direction and maintain this position.

As the rod 4 moves downward, a lug on the rod engages limit switch LS-lwhich then causes valve 56 to be energized to the opened position. Thisaction bypasses the needle valve 53 and admits fluid into mandrel 7 andports 9 and 10 at a a greater rate than before. As an optional mode ofoperation of motor 30, as the limit switch LS-l is closed, the solenoid54b may be energized via switch 57. This causes valve 55 to turnclockwise, exhausting fluid from the upper port 30a of the motor 30 andadmitting pressurizied fluid to the lower port 30b of the motor. Thus,in a very short period of time rod 4 is pulled down, limit switch LS-lis actuated and the rod 4 is urgedupward again.

At the start of a cycle or at any time after a cycle has been completed,the mold 6 may be opened and the mandrel 7 may be withdrawn upward byuse of motor 32. Valve 58 may be turned manually from the rest" positionshown to a position in which pressurized fluid is admitted to port 32bthereby driving motor 32 and mandrel 7 upward to effect a strippingoperation. At this stage, mold 6 and the ram are in their uppermostpositions. They are retracted by de-energizing the power control 45.This energizes solenoids 50b and 42b momentarily, causing valves 49 and41 eachto turn to admit pressurized fluid to the upper ends of motors 35and 29, respectively, and causing them to drive down. The solenoids arethen de-energized which permits the valves 49 and 41 to return to theircentered position with all ports closed. Theextrusion chamber 2 inextrusion barrel 3 is again ready to receive a fresh slug after whichthemandrel 7 may be lowered by'use of motor 32 and valve 58.

Precision control of the movable parts of the apparatus of thisinvention is achieved electronically by the control means shown in FIG.2. For example, immediately after the formation of the head in annulargroove 14, the mold 6 is set in motion at a constant velocity when thevoltage comparison circuit 47 senses a preselected level of voltageoutput at the potentiometer 24 when the ram 15 has gone through. apreselected stroke of about 0.5 to 1.2 inches. In the first increment ofmold motion, the annular bead moves along and over the end of themandrel 7 causing the extrudate to cover the ports 9 and 10. Withcontinued mold motion, the voltage comparison circuit 47 senses adifferent preselected level of voltage from potentiometer 24, triggeringvalve 52 and admitting fluid at a preselected rate through valve 53.This expands part of the neck portion of the extrudate outwardly againstthe mold surface in annular space 21.

As movement of extrusion ram 15 and mold 6 continues, the neck portionis completed and the diverging part of the mold cavity 5 begins to passbeyond the region where the ports 9 and 10 are located, thus permittingnewly extruded plastic to be expanded to a greater degree than in theneck portion as generally shown in FIG. 4. At this stage, when thepolymer has reached, or is beginning to reach, the largest part of themold 6, the ram 4 and rod 28 have advanced to the point where the highpart 23b of the cam 23 drives the potentiometer 51 to a differentposition causing valve 43 to open to a greater degree. This admits fluidat a greater rate to motor 29 which increases the rate of extrusion ofpolymer through orifice 11 and contributes more polymeric material tothe outermost wall of the article being formed.

As the ram 15 nears the end of its stroke, the potentiometer 51 returnsonce again to a lower level position on cam 23 so that the rate ofextrusion of polymer through orifice 11 is decreased; this occurssubstantially as the wall of the article is being completed and thebottom is to be formed and results in a thinner bottom.

Similar precision control is achieved just before the mold comes to astop. The center supporting rod is triggered into action when thevoltage comparison circuit 47 senses a preselected level of voltage frompotentiometer 24 at which point solenoid 54a is energized and valve 55operates admitting fluid to port 30a of motor 30. This starts to pullrod 4 away from abutment with the end of mandrel 7 and causes actuationof limit switch LS-l. This action triggers solenoid valve 56 thusby-passing valve 53 and admitting pressurized fluid to cavity 16 at agreater rate than before. This effects the completion of the expansionof the extruded shape in a shorter time than if valve 53 continued tocontrol the rate of ingress of fluid.

Additionally, if desired, switch 57 may have been closed so thatactuation of switch LS-l would have the added effect of reversing valve55 so that a very short time after its withdrawal, the rod 4 would havethrust toward mandrel 7. The space formerly occupied by the tip of therod 4 is then occupied by polymer which, by this action, is subjected toan impact squeezing effect in coordination with the urging of the ram15. This mode of operation is preferred since the simultaneous actionsresult in a sound, high density closure.

An alternate mode of operation is particularly suited for polymerswhich, after drawing or orienting, exhibit poor conformability to a moldespecially in the final stages of forming a container, in the presentsituation, the blowing and forming of the bottom of the container. Thismode of operation comprises essentially the mode described above with anadded step of reforming the bottom of the container inwardly to form aconcave recess. This is accomplished by the apparatus of FIG. 2 in whichthe voltage comparison circuit 47a is energized optionally by a switch59; the circuit 47a also receives the voltage output of potentiometer 24and is adapted to control down movement of the mold 6 via solenoid 50bof valve 49 in a manner to be described.

As described previously, travel of mold 6 in the upward direction duringthe forming of a container is controlled by voltage comparison circuit47 which, when it senses that the output voltage of potentiometer 24 hasreached a pre-set value, de-energizes solenoid 50a, restoring valve 49to its centered position, thus stopping hydraulic motor 35. Ordinarily,the mold would continue to occupy the position at which it stopped;however, in the presently described mode of operation, at the instantthat the solenoid 50a is deenergized, the voltage comparison circuit 47a(switch 59 closed), receiving the same voltage from potentiometer 24,acts to energize solenoid 50b; the latter actuates valve 49 to admitfluid to port 35b of hydraulic motor 35 thereby driving the mold 6 downagain immediately. The voltage comparison circuit 47a after a short timedelay de-energizes solenoid 50b, the mold 6 having moved through a shortstroke (e.g., about 0.5 inch). When the solenoid 50b is de-energized thevalve 49 becomes centered once again and the mold 6 comes to a stop.

The final steps in the forming of the plastic container, according tothis mode of operation, are shown in FIGS. 8 and 9. In FIG. 8, thecontainer is substantially complete with the mold 6 at the upward limitof its travel except that the plastic wall 60 has not conformed to theentire bottom portion of the mold, leaving a void 61 between plastic andmold. The next step, shown in FIG. 9, comprises moving the mold downwarda short distance (e.g., 0.5 inch) to deform the plastic into a reversebend and to form a truncated conical recess 62 in the bottom portion;during this step the generally conical wall 60' is stretched, impartingadditional orientation to the conical wall 60. It will be realized thatthe next and final step comprises close-off of the aperture occupied bythe tip of the center supporting rod 4, a process step that haspreviously been described. The axial depth of the recess 62 or thedownward stroke of the mold 6 is usually made great enough so that theplastic surface 63, FIG. 10, is either coplanar with the surface 64 oris slightly above it thus assuring stability when the container surface64 rests on a support. The generally conical recess 62 serves thepurpose of increasing the strength of the bottom of the container,improving its ability to resist internal pressures while minimizing theamount of plastic material needed for this purpose.

In operation, the apparatus of this invention is used in the followingmanner: A thermoplastic polymeric slug 1 is placed within the extrusionchamber 2. Extrusion ram 15 is activated so as to force part of thenonmolten thermoplastic polymeric material of the slug 1 through theannular extrusion orifice 11 and into the annular groove 14 in the endof the mold cavity 5. This first stage of extruding an annular bead fromthe thermoplastic slug 1 is shown in FIG. 3. It is seen that the firstpart of the slug 1 to leave the annular extrusion orifice 11 and enterthe annular groove 14 forms a bridge or diaphragm around the entireupper part of the annular space 21 between the outside of the extrusionbarrel 3 and the inside of the mold cavity 5 thereby effecting a seal.The extrusion of the slug into the groove 14 enables, in subsequentsteps, the imposition of axial tension on the extrudate by moving themold to stretch or draw the extrudate.

Immediately after the completion of the formation of the bead within themold cavity 5 and in simultaneous sequence with the continued movementof the extrusion ram 15, the mold 6 is moved at a uniform rate of speedand a fluid such as compressed air or liquid being packaged is forcedthrough into the fluid passage 8, out of the fluid exit ports 9 and 10and into cavity 16. This cavity is formed by the external surface of themandrel 7, the extruded sea] at the annular groove 14 and extruded shape17 which was extruded by the annular extrusion orifice 11 and expandedby the compressed air from the fluid exit ports 9 and 10. This is shownin FIG. 4.

Thus, as mold 6 moves relative to the orifice 11, the bead formed inannular groove 14 anchors the newly formed bottle top to the mold 6 andeffectively moves the fresh extrudate past the compressed air flowingfrom exit ports 9 and 10, thereby causing an almost immediate forcing ofthat extrudate against the wall of mold cavity 5 as it emerges fromorifice 11.

The presently preferred method is centered on the production of athermoplastic article having a nonuniform shell thickness due tothe facethat the rate of extrusion and the speed of the mold are held constantwhile the mold itself has a varying shape. Shell thickness can becontrolled by properly programming the apparatus to obtain either auniform or a non-uniform thickness. Methods of programming shellthickness include varying the speed of the sliding mold or varying theextrusion rate of the slug.

The thermoplastic polymeric material of the slug 1 that is extrudedthrough the annular extrusion orifice 11 becomes partially biaxiallyoriented from the extension operation. The remainder of the desiredbiaxial orientation of the extruded shape 17 is accomplished as theextrudate is drawn and expanded against the surface of the mold cavity 5contained within the mold 6. There is a substantial decrease, e.g., upto 50 percent or more, in wall thickness of the extrudate after it hasbeen drawn and expanded.

The slug 1 continues to be extruded through the annular extrusionorifice 11 by the extrusion ram 15 while the mold 6 moves toward thesecond location over the mandrel 7. The combined action of the extrusionof the slug 1 and-the expansion of the extrudate results inthe desiredshape of the bottle article 18 shown in FIG. 5, but having an unsealedbottom portion as best shown in FIG. 6. The bottom portion of the bottlearticle 18 is sealed by the withdrawal of the center supporting rod 4while the mold 6 stops and the extrusion ram 15 continues to exert aforce on the remaining polymeric material within the extrusion chamber2. This is shown in FIG. 5 with the'completely formed bottle article 19which is in a highly biaxially oriented state.

FIGS. 6 and 7 show in greater detail the preferred bottom sealingoperation in which the partial with drawal of the center supporting rod4 permits polymeric material of the slug, under the continued urging ofthe extrusion ram 15, to flow inward to effect a closure.

Alternatively, the bottom can be sealed according to the processdisclosed in Carmichael, US. Application Ser. No. 57,679, filed July 23,1970, wherein a frictionwelded bottom seal on a thermoplastic bottle iseffected by contacting the bottom of the thermoplastic bottle in thearea immediately adjacent the bottom opening with a rotating frictionsealing head to raise the temperature of the thermo-plastic material toabout its melting point, working the hot thermoplastic material into andsealing the bottom opening, and thereafter quenching the sealed opening.The process can be carried out while the bottle is still in the mold orin a separate operation after the bottle is removed from the mold.

FIG. 7 shows the location of the parts of the apparatus upon thecompletion of the method for forming a hollow article from a hollowslug. In FIG. 7 the center supporting rod 4 has been withdrawn while theextrusion ram 15 depressed the remaining portion of the thermoplasticslug into the volume vacated by the repositioned center supporting rod4.

In an alternate embodiment, the apparatus is modified by providing amoving center rod through the slug instead of a stationary center rod.This permits the use of a closed end or blind hollow thermoplastic slugwherein the closed end becomes the bottom of the article formed,eliminating the need for a separate bottom closure step. In addition,the center rod and slug move at the same rate during extrusion of theslug eliminating relative motion between the slug and the center rod,thereby minimizing the need for lubrication between the center rod andthe slug while reducing the wear in the center rod.

This alternate embodiment is shown in FIGS. 11 to 13 as it is used inthe process of this invention. Referring tov FIG. 11, a hollowcylindrical slug 1a having a closed end 65 is placed in extrusionchamber 2. Mold 6 is positioned in a first location wherein the moldcavity 5 surrounds extrusion chamber 2. Center rod 4a is positionedinside of slug la and extends into fluid passage chamber 8 withinmandrel 7. If desired, the center rod can be heated by conventionalmeans not shown, that in turn heats the thermoplastic slug. Extrusionram 15a is modified to be a solid round bar positioned in extrusionchamber 2 abutting slug la containing the center rod 4a. The center rodis biased against the extrusion ram by conventional means not shown,exerting a nominal force against the extrusion ram sufficient to keepthe extrusion ram from buckling the slug and to insure steady motionduring extrusion. In a typical embodiment, the extrusion ram pressureisabout 13,000

psig and the center rod biasing pressure is about 50 psig. i

In operation, extrusion ram 150 forces slug la out of extrusion chamber2 through extrusion orifice l1 and around mandrel 7. FIG." 12 shows anarticle partially formed, wherein the extrusion ram 15a has forced theslug into the sliding mold while simultaneously moving the centerrodwith the slug so that there is no relative motion between the slug andthe center rod. Fluid is introduced through fluid passageway 8 aroundcenter rod 4a and out through port 10 into the interior portions of theextruded shell 17 forcing it against the mold cavity thereby shaping thearticle.

FIG. 13 shows an article completely formed inside of the mold cavity. Itcan be noted that the bottom of the slug 65 is now the bottom centerportion of the article. In addition, that portion of the center rod 411that originated in the slug while the slug was in the extrusion chamberhas been moved into fluid passageway 8.

After the thermoplastic article is formed, it can be heat treated bywell known processes to increase the crystallinity level, therebydecreasing the ability of the gases to permeate the shell and improvingdimensional stability which is important if the article is used tobottle hot beverages or is to be subjected to high temperatures andpressures in a pasteurization process.

Heat treatment is carried out at temperatures of about 140220 C. andexposure time is relatively short. However, it is generally desirable toconduct the heat treatment for a period of time sufficient to produce adegree of crystallinity in the finished product which is preferably atleast about 30 percent up to 50 percent or more, the maximum attainablecrystallization for polyethylene terephthalate being about 60 percent.In general, especially good results have been observed when this heattreatment step is carried out for a period of about 0.1 to 600 seconds.The upper limit of this treatment is not particularly critical, otherthan from an economical viewpoint, and a duration of treatment of up tominutes is possible.

The thermoplastic slug useful in the present invention is hollow, butthe term hollow, unless otherwise indicated, is meant to include atubelike slug having both ends open, or a tubelike slug having one endopen and one end closed, i.e., a blind slug, wherein the slug is sopositioned in the extrusion barrel that the closed end will form thebottom of the bottle. The tubelike slug having both ends open can be:used with the apparatus incorporating a stationary center rod or amoving center rod but a blind slug can only be used with the apparatusincorporating a movable center rod.

The slug is preferably fabricated by conventional extrusion or injectionmolding methods from thermoplastic materials which are susceptible toincreased strength or reinforcement when biaxially oriented. The slugitself can be oriented or unoriented prior to use. If an oriented slugis used, further orientation occurring in the extrusion drawing andexpansion of the extruded slug is additive in effect. In addition, theslug should be practically amorphous with no more than about 5 percentcrystallinity and clear in appearance. This will result in a clearformed bottle. If it is intended that the bottle be colored, however,the coloring agent such as a dye can be added to the slug formingpolymer and, of course, result in a colored slug.

The dimensions of the slug to be used are determined by many factorsincluding the desired thickness and the desired degree of orientation.Typically the slug is hollow and the radial dimensions are slightlysmaller than the dimensions of the neck of the bottle to be formed ascan be seen in the drawings. The axial length of the slug is slightlyshorter than the dimension between the top and the center of the bottomas measured along the outside of the bottle to be formed. To improve thedimensional stability of the bottle, particularly the radial dimensionsof the neck of the bottle, the slug is initially formed withsubstantially oversized radial dimensions, quenched to a temperaturebelow the crystalline melt point of the polymer, then forced through areducing die slightly smaller than the radial dimensions of the neck ofthe bottle as shown in the drawings. For still further improveddimensional stability, the slug can be compressed in a chambermaintaining the same outside diameter with a tapering mandrel in thecenter of the compression chamber resulting in a very short slug havingan outside diameter slightly smaller than the outside diameter of theneck of the bottle and an inside diameter of practically zero resultingin a very narrow hollow space about the size of a pin hole runningthrough the center of the slug. The compressed slugs are used in theapparatus described above without the presence of the center rod or withthe center rod fully retracted.

The process and apparatus of this invention can be used to preparearticles of various shapes and sizes from various thermoplasticmaterials. The preferred thermoplastic material is polyethyleneterephthalate, and copolymer blends thereof.

One reason polyethylene terephthalate is preferred is because whenoriented, it exhibits excellent strength, creep resistance, and a lowpermeation factor, particularly with respect to carbon dioxide, oxygenand water vapor, making it excellently suited for use as a container forliquids bottled under pressure, such as sodas, beer, or aerosols. Whenforming with polyethylene terephthalate, it is advantageous to startwith essentially amorphous material, i.e., crystallinity no greater thanpercent in order to produce a clear bottle. Useful polyethyleneterephthalate polymers have an inherent viscosity (1 percentconcentration of polymer in a 37.5/62.5 weight percent solution oftetrachloroethane/phenol, respectively, at 30 C.) of at least 0.55.Preferably, the inherent viscosity is at least 0.7, because thisproduces a bottle having significantly improved toughness properties,e.g. increased impact resistance.

Impact resistance is measured by dropping a slug from various heightsonto a concrete floor. In a drop test carried out on 6-inch-long,amorphous polyethylene terephthalate having an inherent viscosity ofabout 1.1 wherein three slugs were used in testing having an averagewall thickness in mils of about 138, 90, and 93, with a weight in gramsof 27.8, 21.2, and 21.6, respectively, each slug sustained two dropsfrom a height of 1 foot, 2 feet, 5 feet and 8 feet without any apparentdamage to the slug and, in addition, each slug sustained the impact of a5-pound weight dropped two times onto the slug from a height of onefoot.

Other useful thermoplastic materials include copolymers ofacrylonitrile/styrene/acrylate; acrylonitrile/methacrylate;methacrylonitrile copolymers; polycarbonates;polybis(para-aminocyclohexyl) dodecaneamide and other poly-amides;polyformaldehyde; high density polyethylene; polypropylene; otherpolyesters and polyvinyl chloride.

. base or bottle-making layers of polymer. Through the use of such aslug, it is possible to produce bottles of base resins with a selectedlamina to be used as (1) a gas barrier, (2) coloring layer, or (3)degrading catalyst.

The extruded slug must be at a temperature within its range of biaxialorientation, i.e., the temperature range for the polymer being usedwherein orientation can occur without line drawing. The heat generatedduring extrusion is generally sufficient for this purpose so that theslug can be extruded at room temperature. However, the orientationtemperature range varies from polymer to polymer, depending on suchfactors as crystallinity, and the glass transition temperature of thepolymer. 1f the orientation range of the polymer is so high that theheat of extrusion is not sufficient to raise the polymer temperature toits orientation range, then the slug can be preheated before extrusion.

The thermoplastic article formed is biaxially oriented and will havephysical properties consistent with the type slug used.

The following examples illustrate the present invention. All parts,precentages and proportions are by weight unless otherwise indicated.

EXAMPLE 1 Polyethylene terephthalate polymer of inherent viscosity about0.96 is made into a hollow cylindrically amorphous shaped slug 4.5inches long, 0.680 inch outside diameter (O.D.) and 0.375 inch insidediameter (l.D.), weighing about 22.6 grams. The slug is preheated toabout 92 C. and extruded through gap T of about 0.033 inch at a barreltemperature of about C. in the apparatus described above. The velocityof the ram 15 is about 3.6 inches per second and the velocity of themold 6 is about 5.1 inches per second. Air at about 255 psig pressure isintroduced through ports 9 and 10. The internal mold diameter is about2.5 inches.

A bottle is formed having a wall thickness of about 11.4 mils; the axialtensile strength is about 16,500 psi and the hoop tensile strength isabout 26,700 psi.

EXAMPLE 2 Example 1 is repeated except as follows:

Inherent viscosity 1.0

Slug length 6.5 inches Slug O.D. 0.680 inch Slug [.D. 0.477 inch Slugweight 23.5 grams Preheat temp. C. Barrel temp. 30-100C. Gap 0.035 inchRam velocity 5 in.lsec. Mold velocity 5.8 in./sec. Air Pressure 350 psiTensile (axial) 8,000 psi Tensile (hoop) 30,300 psi Wall thickness 16.8mils EXAMPLE 3 A thermoplastic bottle is produced according to theprocedure of Example 1, namely extruding and blowmolding a hollowcylindrically shaped slug 4.5 inches long with an outside diameter of0.680 inch and an inside diameter of 0.375 inch weighing about 22.6grams. The slug is made from polyethylene terephthalate which has aninherent viscosity of 0.91. The slug has a density on the outsidesurface of 1.332 and on the inside surface of 1.334, and a crystallinityof about 5 percent.

The bottle exhibits the following properties: 1 Density andCrystallinity of Polymer from Various Points on the Bottle CrystallinityDensity Neck 1.332 0 Top of major cylindrical section 1.345 6 Middle ofmajor cylindrical section 1.356 17 Bottom of major cylindrical section1.361 22 Bottom of bottle 1.332 0 ll Tensile Properties (Right CylinderAxial Hoop Section) Tensile strength (kpsi) 7.8 23.8 Elongation 59 17Tensile modulus (kpsi) 246 683 Yield stress (kpsi) 7.6 kpsi Ill BiaxialOrientation (Right Cylinder Section) X-Ray Orientation Angles 26 peakdirection of rotation Orientation Peak (chi) (phi) Angle Max. 17.0 planeperpendicular 83 (Axial) 0X to beam plane parallel to beam Scan 90 52(Hoop) 0X 0 Scan 66 (Hoop) 0X 27,0 Plane perpendicular to beam Scan 0Plane parallel to beam Scan 90 32 (Hoop) 5X 0 Scan 40 (Hoop) 8711)Considering the X-ray orientation angles and the tensile propertiesabove, the bottle exhibits an effective stretch ratio of about 3.5 timesin the hoop direction and about 1.25 times in the axial direction.

N Permeability (Right Cylinder Section) stress of 5,000 psi with creepat 100 hours at a value less than 2 percent and long term creep of days,less than 5 percent. This corresponds to a deformation constant of about1.5.

As many widely different embodiments of this invention may be madewithout departing from the spirit and scope thereof, it is to beunderstood that this invention is not limited to the specificembodiments thereof except as defined in the appended claims, and allchanges which come within the meaning and range of equivalence areintended to be embraced herein.

We claim:

1. An apparatus for forming a thermoplastic article from a blind,hollow, cylindrical thermoplastic slug comprised of:

a. a slidable mold having a cavity shaped to produce the article;

b. an annular extrusion orifice located within the mold cavity whereinthe extrusion orifice is formed by the confronting end portions of astationary annular extrusion barrel having an internal bore forreceiving the blind slug and a stationary mandrel in axial alignmentwith the extrusion barrel;

0. means for extruding the slug open end first through the annularextrusion orifice into the mold wherein the extrusion means includes amovable center rod in axial alignment with and contained within themandrel and the extrusion barrel forming a closefitting extrusionchamber in theextrusion barrel wherein the hollow slug can be placed inthe extrusion chamber with the center rod running into the hollow slugcontacting the inside surface of the slug to support the walls of theslug during extrusion and an extrusion ram inside of the extrusionbarrel to contact the outside surface of the blind end of the slug andforce the slug out through the extrusion orifice while simultaneouslymoving the center rod inside of the slug into the mandrel in thedirection of extrusion;

(1. means in the mold to accept and hold the extrudate at one end of themold cavity;

e. means for sliding the mold from a first location to a second locationrelative to the extrusion orifice while the slug is continuouslyextruded, drawing the extruded slug into the interior of the moldforming a hollow shell out of the extrudate; and

f. means for introducing a fluid under pressure against the interior ofthe hollow shell, while the slug is simultaneously being extruded anddrawn, to expand the hollow shell of extrudate against the interior ofthe mold.

2. The apparatus of claim 1 in which the mold has a cavity shaped toreproduce a generally cylindrical bottle.

3. The annular extrusion orifice of claim 1 formed by the confrontingend portions of the extrusion barrel and the mandrel wherein theconfronting end portions have a curving shape so that in thecross-sectional profile, taken coplanar with the central axis ofextrusion, the annular orifice in the direction of extrusion is areaconvergent.

4. The annular extrusion orifice of claim 3 wherein the cross-sectionalarea of the annular orifice, taken perpendicular to the central axis ofextrusion, remains the same in value in the direction of extrusion.

5. The annular extrusion orifice of claim 3 wherein the cross-sectionalarea of the annular orifice, taken perpendicular to the central axis ofextrusion, decreases in value in the direction of extrusion.

6. The apparatus of claim 1 in which the means for introducing a fluidinto the interior of the hollow shell is a mandrel of uniform externaldiameter positioned within the mold and axially aligned with theextrusion barrel and having an internal fluid passageway terminating inexhaust ports located at the end of the mandrel next adjacent theannular orifice.

7. The apparatus of claim 1 including additional means to reverse thedirection of the sliding mold after completion of drawing and expandingthe extrudate, forming a recess in the bottom of the article.

8. The apparatus of claim 1 including means for varying the speed of themold.

9. The apparatus of claim 1 including means for varying the rate ofextrusion.

10. The apparatus of claim 1 including means for simultaneously varyingboth the speed of the mold and the rate of extrusion.

11. The apparatus of claim 1 including means for cooling the mold.

12. The apparatus of claim 1 including means to preheat the slug beforethe slug is extruded.

13. An apparatus for forming a thermoplastic article from a hollow,cylindrical thermoplastic slug having both ends open comprised of:

a. a slidable mold having a cavity shaped to produce the article;

b. an annular extrusion orifice located within the mold cavity whereinthe annular extrusion orifice is formed by the confronting end portionsof a stationary extrusion barrel having an internal bore for receivingthe hollow thermoplastic slug, and a stationary mandrel in axialalignment with the extrusion barrel means for extruding the slug openend first through the annular extrusion orifice wherein the extrusionmeans includes a center rod in axial alignment with and contained withinthe extrusion barrel forming a close-fitting extrusion chamber whereinthe hollow slug can be placed in the extrusion chamber with the centerrod running through the hollow slug to support the walls of the slugduring extrusion, and a ram inside of the extrusion barrel to contactthe slug and force the slug around the center rod through the extrusionorifice without moving the center rod,

d. means in the mold to accept and hold the extrudate at one end of themold cavity;

e. means for sliding the mold from a first location to a second locationrelative to the extrusion orifice while the slug is continuouslyextruded, drawing the extruded slug into the interior of the moldforming a hollow shell out of the extrudate; and

f. means for introducing a fluid against the interior of the hollowshell while the slug is simultaneously being extruded and drawn toexpand the hollow shell of extrudate against the interior of the mold.

14. The apparatus of claim 13 for forming a thermoplastic article from ahollow, cylindrical thermoplastic slug having both ends open andincluding additional means to withdraw the center rod and means to urgethe trailing edges of the slug radially inward to the bottom center ofthe article forming an integral closure.

15. The apparatus of claim 13 in which the mold has a cavity shaped toreproduce a generally cylindrical bottle.

16. The apparatus of claim 13 wherein the annular extrusion orifice isformed by (a) a stationary extrusion barrel having an internal bore forreceiving the hollow thermoplastic slug, (b) a stationary mandrel inaxial alignment with and confronting the extrusion barrel wherein theannualr extrusion orifice is formed by the confronting end portions ofthe extrusion barrel and the mandrel.

17. The annular extrusion orifice of claim 13 formed by the confrontingend portions of the extrusion barrel and the mandrel where theconfronting end portions have a curving shape so that in thecross-sectional profile, taken parallel to the central axis of extrusionthe annular orifice in the direction of extrusion is area convergent.

18. The annular extrusion orifice of claim 13 wherein thecross-sectional area of the annular orifice, taken perpendicular to thecentral axis of extrusion, remains the same in value in the direction ofextrusion.

19. The annular extrusion orifice of claim 13 wherein thecross-sectional area of the annular orifice, taken perpendicular to thecentral axis of extrusion, decreases in value in the direction ofextrusion.

20. The apparatus of claim 13 wherein the annular extrusion orifice andthe means for extruding the hollow thermo-plastic slug are:

a. a stationary annular extrusion barrel having an internal bore forreceiving the slug,

b. a stationary mandrel in axial alignment with the extrusion barrel andconfronting the extrusion barrel,

c. an annular extrusion orifice formed by the confronting end portionsof the extrusion barrel and the mandrel,

d. a movable center rod in axial alignment with and contained within themandrel and the extrusion barrel forming a close-fitting extrusionchamber in the extrusion barrel wherein the hollow slug can be placed inthe extrusion chamber with the center rod running into the hollow slugcontacting the inside surface of the slug to support the walls of theslug during extrusion, and

e. an extrusion ram inside of the extrusion barrel to contact the slugand force the slug out through the extrusion orifice whilesimultaneously moving the center rod inside of the slug into the mandrelin the direction of extrusion.

21. The apparatus of claim 13 in which the means for introducing a fluidinto the interior of the hollow shell is a mandrel of uniform externaldiameter positioned within the mold and axially aligned with theextrusion barrel and having an internal fluid passageway terminating inexhaust ports located at the end of the mandrel next adjacent theannular orifice.

22. The apparatus of claim 13 including additional means to reverse thedirection of the sliding mold after completion of drawing and expandingthe extrudate, forming a recess in the bottom of the article.

23. The apparatus of claim 13 including means for varying the speed ofthe mold.

24. The apparatus of claim 13 including means for varying the rate ofextrusion.

25. The apparatus of claim 13 including means for simultaneously varyingboth the speed of the sliding mold and the rate of extrusion.

26. The apparatus of claim 13 including means for cooling the mold.

27. The apparatus of claim 13 including means to preheat the slug beforethe slug is extruded.

28. An apparatus for forming a thermoplastic article from a blind,hollow thermoplastic slug comprised of:

a. a slidable mold having a cavity shaped to produce the article;

b. an annular extrusion orifice located within the mold cavity whereinthe extrusion orifice is formed by the confronting end portions of astationary annular extrusion barrel having an internal bore forreceiving the blind slug and a stationary mandrel in axial alignmentwith the extrusion barrel;

c. means for extruding the slug into the mold wherein the meanscomprises a movable center rod in axial alignment with and containedwithin the mandrel and the extrusion barrel, forming a close-fittingextrusion chamber in the extrusion barrel wherein the hollow slug can beplaced in the extrusion chamber with the center rod running into thehollow slug contacting the inside surface of the slug to support thewalls of the slug during extrusion and an extrusion ram inside of theextrusion barrel to contact the outside surface of the blind end of theslug and force the slug out through the extrusion orifice whilesimultaneously moving the center rod inside of the slug into the mandrelin the direction of extrusion;

d. means for sliding the mold from a first location to a second locationrelative to the extrusion orifice while the slug is continuouslyextruded, drawing the extrudate into the interior of the mold forming ahollow shell out of the extrudate; and

e. means for introducing a fluid against the interior of the hollowshell while the slug is simultaneously being extruded and drawn toexpand the hollow shell of extrudate against the interior of the mold.

29. The apparatus of claim 28 for forming a thermoplastic article from ahollow thermoplastic slug having both ends open including the additionof means to urge the trailing edges of the slug radially inward to thebottom center of the article forming an integral closure.

30. An apparatus for forming a thermoplastic article from a hollowthermoplastic slug comprised of:

a. a mold having a cavity shaped to produce the article;

b. an annular extrusion orifice located within the mold cavity whereinthe extrusion orifice is formed by the confronting end portions of anannular extrusion barrel having an internal bore for receiving the slugand a mandrel in axial alignment with the extrusion barrel;

c. means for extruding the slug through the annular extrusion orificeinto the mold wherein the extrusion means includes a center rod in axialalignment with and contained within the extrusion barrel, forming aclose-fitting extrusion chamber in the extrusion barrel wherein thehollow slug can be placed in the extrusion chamber with the center rodrunning into the hollow slug contacting the inside of the slug tosupport the walls of the slug during extrusion and an extrusion raminside of the extrusion barrel to contact one end of the slug and forcethe slug through the extrusion orifice;

d. means for relative sliding movement between the mold and theextrusion orifice while the slug is continuously extruded, drawing theextrudate into the interior of the mold forming a hollow shell out ofthe extrudate; and

e. means for introducing a fluid under pressure against the interior ofthe hollow shell, while the slug is simultaneously being extruded anddrawn, to expand the hollow shell of extrudate against the interior ofthe mold.

31. An apparatus for forming a "thermoplastic article from a blind,hollow thermoplastic slug comprised of:

a. a mold having a cavity shaped to produce the article;

b. an annular extrusion orifice located within the mold cavity whereinthe extrusion orifice is formed by the confronting end portions of anannular extrusion barrel having an internal bore for receiving the blindslug and a mandrel in axial alignment with the extrusion barrel;

0. means for extruding the slug into the mold wherein the meanscomprises a movable center rod in axial alignment with and containedwithin the mandrel and the extrusion barrel, forming a close-fittingextrusion chamber in the extrusion barrel wherein the hollow slug can bepalced in the extrusion chamber with the center rod running into thehollow slug contacting the inside surface of the slug to support thewalls of the slug during extrusion and an extrusion rarn inside of theextrusion barrel to contact the outside surface of the blind end of theslug and force the slug out through the extrusion orifice;

d. means for relative sliding movement between the mold and theextrusion orifice while the slug is continuously extruded, drawing theextrudate into the interior of the mold forming a hollow shell out ofthe extrudate; and

e. means for introducing a flluid under pressure against the interior ofthe hollow shell, while the slug is simultaneously being extruded anddrawn, to expand the hollow shell of extrudate against the interior ofthe mold.

1. An apparatus for forming a thermoplastic article from a blind,hollow, cylindrical thermoplastic slug comprised of: a. a slidable moldhaving a cavity shaped to produce the article; b. an annular extrusionorifice located within the mold cavity wherein the extrusion orifice isformed by the confronting end portions of a stationary annular extrusionbarrel having an internal bore for receiving the blind slug and astationary mandrel in axial alignment with the extrusion barrel; c.means for extruding the slug open end first through the annularextrusion orifice into the mold wherein the extrusion means includes amovable center rod in axial alignment with and contained within themandrel and the extrusion barrel forming a close-fitting extrusionchamber in the extrusion barrel wherein the hollow slug can be placed inthe extrusion chamber with the center rod running into the hollow slugcontacting the inside surface of the slug to support the walls of theslug during extrusion and an extrusion ram inside of the extrusionbarrel to contact the outside surface of the blind end of the slug andforce the slug out through the extrusion orifice while simultaneouslymoving the center rod inside of the slug into the mandrel iN thedirection of extrusion; d. means in the mold to accept and hold theextrudate at one end of the mold cavity; e. means for sliding the moldfrom a first location to a second location relative to the extrusionorifice while the slug is continuously extruded, drawing the extrudedslug into the interior of the mold forming a hollow shell out of theextrudate; and f. means for introducing a fluid under pressure againstthe interior of the hollow shell, while the slug is simultaneously beingextruded and drawn, to expand the hollow shell of extrudate against theinterior of the mold.
 2. The apparatus of claim 1 in which the mold hasa cavity shaped to reproduce a generally cylindrical bottle.
 3. Theannular extrusion orifice of claim 1 formed by the confronting endportions of the extrusion barrel and the mandrel wherein the confrontingend portions have a curving shape so that in the cross-sectionalprofile, taken coplanar with the central axis of extrusion, the annularorifice in the direction of extrusion is area convergent.
 4. The annularextrusion orifice of claim 3 wherein the cross-sectional area of theannular orifice, taken perpendicular to the central axis of extrusion,remains the same in value in the direction of extrusion.
 5. The annularextrusion orifice of claim 3 wherein the cross-sectional area of theannular orifice, taken perpendicular to the central axis of extrusion,decreases in value in the direction of extrusion.
 6. The apparatus ofclaim 1 in which the means for introducing a fluid into the interior ofthe hollow shell is a mandrel of uniform external diameter positionedwithin the mold and axially aligned with the extrusion barrel and havingan internal fluid passageway terminating in exhaust ports located at theend of the mandrel next adjacent the annular orifice.
 7. The apparatusof claim 1 including additional means to reverse the direction of thesliding mold after completion of drawing and expanding the extrudate,forming a recess in the bottom of the article.
 8. The apparatus of claim1 including means for varying the speed of the mold.
 9. The apparatus ofclaim 1 including means for varying the rate of extrusion.
 10. Theapparatus of claim 1 including means for simultaneously varying both thespeed of the mold and the rate of extrusion.
 11. The apparatus of claim1 including means for cooling the mold.
 12. The apparatus of claim 1including means to preheat the slug before the slug is extruded.
 13. Anapparatus for forming a thermoplastic article from a hollow, cylindricalthermoplastic slug having both ends open comprised of: a. a slidablemold having a cavity shaped to produce the article; b. an annularextrusion orifice located within the mold cavity wherein the annularextrusion orifice is formed by the confronting end portions of astationary extrusion barrel having an internal bore for receiving thehollow thermoplastic slug, and a stationary mandrel in axial alignmentwith the extrusion barrel c. means for extruding the slug open end firstthrough the annular extrusion orifice wherein the extrusion meansincludes a center rod in axial alignment with and contained within theextrusion barrel forming a close-fitting extrusion chamber wherein thehollow slug can be placed in the extrusion chamber with the center rodrunning through the hollow slug to support the walls of the slug duringextrusion, and a ram inside of the extrusion barrel to contact the slugand force the slug around the center rod through the extrusion orificewithout moving the center rod, d. means in the mold to accept and holdthe extrudate at one end of the mold cavity; e. means for sliding themold from a first location to a second location relative to theextrusion orifice while the slug is continuously extruded, drawing theextruded slug into the interior of the mold forming a hollow shell outof the extrudate; and f. means for introducing a fluid against theinterior of the hollow shell whiLe the slug is simultaneously beingextruded and drawn to expand the hollow shell of extrudate against theinterior of the mold.
 14. The apparatus of claim 13 for forming athermoplastic article from a hollow, cylindrical thermoplastic slughaving both ends open and including additional means to withdraw thecenter rod and means to urge the trailing edges of the slug radiallyinward to the bottom center of the article forming an integral closure.15. The apparatus of claim 13 in which the mold has a cavity shaped toreproduce a generally cylindrical bottle.
 16. The apparatus of claim 13wherein the annular extrusion orifice is formed by (a) a stationaryextrusion barrel having an internal bore for receiving the hollowthermoplastic slug, (b) a stationary mandrel in axial alignment with andconfronting the extrusion barrel wherein the annualr extrusion orificeis formed by the confronting end portions of the extrusion barrel andthe mandrel.
 17. The annular extrusion orifice of claim 13 formed by theconfronting end portions of the extrusion barrel and the mandrel wherethe confronting end portions have a curving shape so that in thecross-sectional profile, taken parallel to the central axis of extrusionthe annular orifice in the direction of extrusion is area convergent.18. The annular extrusion orifice of claim 13 wherein thecross-sectional area of the annular orifice, taken perpendicular to thecentral axis of extrusion, remains the same in value in the direction ofextrusion.
 19. The annular extrusion orifice of claim 13 wherein thecross-sectional area of the annular orifice, taken perpendicular to thecentral axis of extrusion, decreases in value in the direction ofextrusion.
 20. The apparatus of claim 13 wherein the annular extrusionorifice and the means for extruding the hollow thermo-plastic slug are:a. a stationary annular extrusion barrel having an internal bore forreceiving the slug, b. a stationary mandrel in axial alignment with theextrusion barrel and confronting the extrusion barrel, c. an annularextrusion orifice formed by the confronting end portions of theextrusion barrel and the mandrel, d. a movable center rod in axialalignment with and contained within the mandrel and the extrusion barrelforming a close-fitting extrusion chamber in the extrusion barrelwherein the hollow slug can be placed in the extrusion chamber with thecenter rod running into the hollow slug contacting the inside surface ofthe slug to support the walls of the slug during extrusion, and e. anextrusion ram inside of the extrusion barrel to contact the slug andforce the slug out through the extrusion orifice while simultaneouslymoving the center rod inside of the slug into the mandrel in thedirection of extrusion.
 21. The apparatus of claim 13 in which the meansfor introducing a fluid into the interior of the hollow shell is amandrel of uniform external diameter positioned within the mold andaxially aligned with the extrusion barrel and having an internal fluidpassageway terminating in exhaust ports located at the end of themandrel next adjacent the annular orifice.
 22. The apparatus of claim 13including additional means to reverse the direction of the sliding moldafter completion of drawing and expanding the extrudate, forming arecess in the bottom of the article.
 23. The apparatus of claim 13including means for varying the speed of the mold.
 24. The apparatus ofclaim 13 including means for varying the rate of extrusion.
 25. Theapparatus of claim 13 including means for simultaneously varying boththe speed of the sliding mold and the rate of extrusion.
 26. Theapparatus of claim 13 including means for cooling the mold.
 27. Theapparatus of claim 13 including means to preheat the slug before theslug is extruded.
 28. An apparatus for forming a thermoplastic articlefrom a blind, hollow thermoplastic slug comprised of: a. a slidable moldhaving a cavity shaped to produce the artIcle; b. an annular extrusionorifice located within the mold cavity wherein the extrusion orifice isformed by the confronting end portions of a stationary annular extrusionbarrel having an internal bore for receiving the blind slug and astationary mandrel in axial alignment with the extrusion barrel; c.means for extruding the slug into the mold wherein the means comprises amovable center rod in axial alignment with and contained within themandrel and the extrusion barrel, forming a close-fitting extrusionchamber in the extrusion barrel wherein the hollow slug can be placed inthe extrusion chamber with the center rod running into the hollow slugcontacting the inside surface of the slug to support the walls of theslug during extrusion and an extrusion ram inside of the extrusionbarrel to contact the outside surface of the blind end of the slug andforce the slug out through the extrusion orifice while simultaneouslymoving the center rod inside of the slug into the mandrel in thedirection of extrusion; d. means for sliding the mold from a firstlocation to a second location relative to the extrusion orifice whilethe slug is continuously extruded, drawing the extrudate into theinterior of the mold forming a hollow shell out of the extrudate; and e.means for introducing a fluid against the interior of the hollow shellwhile the slug is simultaneously being extruded and drawn to expand thehollow shell of extrudate against the interior of the mold.
 29. Theapparatus of claim 28 for forming a thermo-plastic article from a hollowthermoplastic slug having both ends open including the addition of meansto urge the trailing edges of the slug radially inward to the bottomcenter of the article forming an integral closure.
 30. An apparatus forforming a thermoplastic article from a hollow thermoplastic slugcomprised of: a. a mold having a cavity shaped to produce the article;b. an annular extrusion orifice located within the mold cavity whereinthe extrusion orifice is formed by the confronting end portions of anannular extrusion barrel having an internal bore for receiving the slugand a mandrel in axial alignment with the extrusion barrel; c. means forextruding the slug through the annular extrusion orifice into the moldwherein the extrusion means includes a center rod in axial alignmentwith and contained within the extrusion barrel, forming a close-fittingextrusion chamber in the extrusion barrel wherein the hollow slug can beplaced in the extrusion chamber with the center rod running into thehollow slug contacting the inside of the slug to support the walls ofthe slug during extrusion and an extrusion ram inside of the extrusionbarrel to contact one end of the slug and force the slug through theextrusion orifice; d. means for relative sliding movement between themold and the extrusion orifice while the slug is continuously extruded,drawing the extrudate into the interior of the mold forming a hollowshell out of the extrudate; and e. means for introducing a fluid underpressure against the interior of the hollow shell, while the slug issimultaneously being extruded and drawn, to expand the hollow shell ofextrudate against the interior of the mold.
 31. An apparatus for forminga thermoplastic article from a blind, hollow thermoplastic slugcomprised of: a. a mold having a cavity shaped to produce the article;b. an annular extrusion orifice located within the mold cavity whereinthe extrusion orifice is formed by the confronting end portions of anannular extrusion barrel having an internal bore for receiving the blindslug and a mandrel in axial alignment with the extrusion barrel; c.means for extruding the slug into the mold wherein the means comprises amovable center rod in axial alignment with and contained within themandrel and the extrusion barrel, forming a close-fitting extrusionchamber in the extrusion barrel wherein the hollow slug can be palced inthe extrusion chamber with the centEr rod running into the hollow slugcontacting the inside surface of the slug to support the walls of theslug during extrusion and an extrusion ram inside of the extrusionbarrel to contact the outside surface of the blind end of the slug andforce the slug out through the extrusion orifice; d. means for relativesliding movement between the mold and the extrusion orifice while theslug is continuously extruded, drawing the extrudate into the interiorof the mold forming a hollow shell out of the extrudate; and e. meansfor introducing a fluid under pressure against the interior of thehollow shell, while the slug is simultaneously being extruded and drawn,to expand the hollow shell of extrudate against the interior of themold.